Robina Li

Graph algorithms are among the most versatile tools in competitive programming and coding interviews. A graph is simply a collection of nodes (vertices) connected by edges, and nearly every “network,”...

Dynamic Programming is the most common pattern in LeetCode Medium/Hard problems. If you only learn one advanced technique, make it DP.

This page is your toolbox of essential data structures for LeetCode. Each template is self-contained C++ you can copy directly into your solution. They range from beginner-friendly (binary search, prefix...

Arrays and strings are the foundation of coding interviews — you’ll encounter them in nearly every problem set. This page provides battle-tested Java templates for the most important patterns: sliding...

This page covers specialized algorithmic techniques that appear in Hard-level LeetCode problems and competitive programming. These are not everyday patterns — most interviews won’t require them — but when a...

LeetCode Categories and Solution Templates

Given a binary array bits that ends with 0, determine whether the last character must be a 1-bit character.

Reverse the array of characters s in-place using O(1) extra memory.

Difficulty: Medium Category: Linked List, Circular List Companies: Amazon, Facebook, Google, Microsoft

Difficulty: Medium Category: Stack, Parsing, Simulation Companies: Amazon, Facebook, Google, Twitter